Field of Invention
The present invention relates to an optical element. More particularly, the present invention relates to an optical lens, a backlight module and a display device.
Description of Related Art
In order to meet the requirements of lightness and thinness for a direct type backlight module, a conventional method is to decrease a light-mixing distance of a secondary lens in the direct type backlight modules or to increase the number of the light-emitting diodes disposed therein.
The secondary lens mainly includes a refracting type lens and a reflecting type lens. A light-emitting angle of the refracting type lens is only about 75 degrees, and thus, the too large distance between any two adjacent light-emitting diodes (i.e. a LED pitch) will result in the problem of poor illumination uniformity. On the other hand, although the light-emitting angle of the reflecting type lens is larger than 90 degrees, yet the light-incident surface and the light-emitting surface of the reflecting type lens have to be designed as complicated curved surfaces. Because the formation of the complicated curved surfaces requires high precision, the manufacturing cost thereof is expensive. In addition, the reflecting type lens cannot be formed accurately due to the complicated curved surfaces, thus affecting its light-emitting effect.